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A case for why DNA evidence must always be questioned

In any case involving criminal charges, the prosecution must be able to present compelling evidence and facts. Today, many prosecutors in criminal cases rely heavily on DNA evidence which is often presented as being irrefutable. In reality, however, there are numerous factors that must be taken into account when considering the validity and reliability of DNA evidence including how such evidence was gathered, handled and tested.

In 1983 scientists and forensic experts began using a process known as polymerase chain reaction or PCR to copy and replicate trance samples of DNA material so such material could more easily be studied and tested. While the process is certainly useful from a historical perspective with regard to studying remains and artifacts from long ago, problems can arise when PCR technology is used to replicate DNA evidence in criminal cases.

The problem, many forensic experts contend, is that PCR works almost too well for replicating even trace or low level amounts of DNA material. Consequently it's highly likely that in addition to the targeted DNA material, DNA samples from multiple other individuals are also replicated thereby contaminating and changing the source material. In cases where tainted DNA material is presented as evidence in a criminal trial, innocent individuals may end up paying the price.

One vocal critic of the use of PCR technology in criminal cases is the former director of New York City's Forensic Toxicology Laboratory who recently filed a lawsuit against the city alleging that she was forced into retirement after questioning the city's reliance on PCR-manipulated DNA data in criminal prosecutions.

Critics of PCR technology argue that such evidence should never be admitted in the courtroom as the methodology "involves too much subjectivity and even guessing, and could lead to wrongful convictions."

Currently, the state of Massachusetts does use PCR technology to replicate DNA data that is subsequently used in the prosecution of criminal cases. Still, as the controversy over the use of PCR proves, DNA evidence is never 100 percent reliable and the methods by which such evidence is collected, handled, tested and stored should always be investigated and considered in any criminal defense case.

Source: The New York Times, "DNA Under the Scope, and a Forensic Tool Under a Cloud," Carl Zimmer, Feb. 26, 2016

The New York Times, "Ex-Official Says Medical Examiner Forced Her Out Over DNA Technique," Benjamin Weiser and Joseph Goldstein, Feb. 18, 2016

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A case for why DNA evidence must always be questioned | Anthony M. Salerno, P.C.